1. Field of the Invention
This invention relates to a recording apparatus, and more particularly to a recording apparatus which permits a recording medium to be replaced with another recording medium
2. Description of the Prior Art
The known recording apparatuses include the kind having a movable head for recording on a rotary recording medium, such as a magnetic disc or a magnetic cylinder, a unit length of information (such as one field or one frame portion of a video signal or the like) in each of recording tracks which are formed in a concentric circular shape or in an annular shape on the recording medium accordingly, as the information is recorded. In preventing overlapped recording in recording the information with the apparatus of this kind, for example, the head must be first accurately positioned at an unrecorded part of the recording medium. In accordance with a known method employed in the conventional apparatus, a desired recording position of the head on the recording medium is checked for the presence or absence of any previous record there before recording. In the event of the presence of a previous record, the head is shifted to a next desired recording position. The head is thus positioned at an unrecorded part of the recording medium with such a check-up process repeated before recording. An example of this method is disclosed in Japanese Laid-Open Patent Application No. SHO 54 -140515.
In the recording apparatus arranged in this manner, with a control sequence arranged to include a process of shifting the head to a next recording position either upon completion of recording in one position or at the start of a next recording process, the present recording position of the head on the recording medium serves as a datum point for determining the next recording position on the medium. Therefore, even in cases where the power supply is switched off or where, in the event of a portable apparatus, the power source battery is taken out for replacement or for charging or where the battery voltage drops below a threshold value and becomes unserviceable, the head can be shifted accurately to the next position on the same recording medium in relation to the present head position when the power supply is again switched on or has recovered its voltage, unless in the meantime the head is shifted to some other position. Such an accurate shift of the head position enables the apparatus to resume a recording operation without overlapping the record nor leaving any unnecessary unrecorded part (blank tracks).
However, if the recording medium is replaced with another recording medium while the power supply is off due to some reason as mentioned above, the present head position becomes meaningless and is no longer usable as a datum point. Then, resumption of recording under that condition either results in overlapped recording or blank recording tracks. To avoid this trouble, the above-stated process of positioning the head for an unrecorded part on the recording medium must be carried out every time the power supply is switched on. However, since the fact that the recording medium has been replaced is not confirmed, this method is unreasonable. Besides, this method deprives the apparatus of prompt recording under all conditions. Further, in the event of a portable apparatus, the method presents a serious problem as it quickens the consumption of the power supply battery.
Problems similar to the above-stated ones are likely to occur also in recording apparatuses of other kinds arranged to shift recording conditions, such as switching use of one head over to another according to the properties or kind of the recording medium.